WIYN 3.5m Observatory

NESSI

The NN-Explore Exoplanet Stellar Speckle Imager, or NESSI, utilizes two electron-multiplying CCD cameras to simultaneously capture speckle images in two channels split by a dichroic at 686.4nm. Speckle observations provide resolutions at or near the diffraction limit of the telescope, allowing detection of faint companions to target stars with relative astrometry and photometric characterization with a contrast level of approximately 5 magnitudes.

NESSI is primarily operated in queue mode at WIYN where it is most frequently utilized by NN-Explore observing programs. Targets include known or candidate exoplanet host stars that are scrutinized for secondary or other nearby sources and other stellar samples of interest to the exoplanet or stellar astronomy communities. NESSI also has unique capabilities for doing high speed photometry or other observations that can utilize its unusual plate scales.

NESSI's EMCCDs can operate with high sensitivity and low readnoise, even at very fast readout rates. The maximum frame rate for imaging over the full 1024x1024 pixel detectors with no binning is 26fps (38ms exposures). By using subwindows and binning, the cameras can operate at higher frame rates.

For diffraction-limited speckle imaging, NESSI operates with a 19x19 arcsec field of view and 0.018 arcsec/pixel plate scale. NESSI can also switch on the fly to its "wide-field" mode which expands the field of view beyond 70 arcseconds. Each 6-slot filter wheel comes with two ~40nm wide speckle filters. SDSS ugriz filter occupy other slots.

Further information on NESSI can be found on these web pages.

NESSI Characteristics

	Wide Field Mode	Speckle Mode
Telescope Focal Plane:
Telescope f/#:	6.289	6.289
Plate Scale:	9.374 arcsec/mm	9.374 arsec/mm
Focal Lengths:
L1 Focal Length:	100mm	30mm
L2 Focal Length:	150mm	200mm
Optical Path:
Tel. Focus:	0mm = 0in	0mm = 0in
L1:	100mm = 3.937in	30mm = 1.181in
L2:	258.4mm = 10.173in	278.4mm = 10.961in
Detector:	150mm = 5.906	200mm = 7.874in
Total Length:	508.4mm = 20.016in	508.4mm = 20.016in
Detector Image Plane:
Magnification from Tel. focal plane:	1.5x	6.67x
Pixel Scale (13 micron pixels):	0.0813 arsec/pix	0.0182 arsec/pix
Unvignetted Circle Dia.:	56 arcsec	22 arcsec
Square Detector FOV:	83 x 83 arcsec	19 x 19 arcsec

NESSI Detectors

	1024 x 1024 pixel electron multiplying CCDs (Andor Ixon Ultra 888's).
	The electron multiplying aspect of EMCCs allows imaging at higher speeds than traditional CCDs because the readnoise is effectively lowered.
	High speeds are also made possible through shutterless operation in a frame transfer mode.

NESSI Filters

Filter Wheel A	Centeral λ, bandwidth	Filter Wheel B	Central λ, bandwidth
SDSS/u	354.3nm, 32.7nm	SDSS/i	765.4nm, 146.4nm
SDSS/g	480nm, 151.1nm	SDSS/z	943.3nm, 242.7nm
SDSS/r	620nm, 143.5nm	716	716nm, 51.5nm
467	467.1nm, 44nm	832	832nm, 40.4nm
562	562.3nm, 43.6nm